Multi-Band Observation Receiver

ABSTRACT

Transmitter observation receivers and methods are described that can predistortion-compensate transmitters capable of operating in multiple communication bands and frequency ranges. Such observation receivers and method involve generating at least one compensation signal such that a signal to be transmitted that is within a bandwidth that simultaneously encompasses multiple frequency ranges is compensated.

TECHNICAL FIELD

This invention relates to electronic communication systems and moreparticularly to pre-distortion-compensated transmitters in such systemsand even more particularly to observation receivers and techniques insuch transmitters.

BACKGROUND

Many current electronic communication systems use quadrature modulationschemes, which involve in-phase (I) and quadrature (Q) signal componentsand do not have constant envelopes. Examples of such communicationsystems are cellular radio telephone systems that use wideband codedivision multiple access (WCDMA), orthogonal frequency division multipleaccess (OFDMA), and their variants. Thus, part of the communicatedinformation is encoded in the amplitude (envelope) of the transmittedsignal and part is encoded in the phase of the transmitted signal.

To avoid distorting communicated information, the power amplifier (PA)and various other components of a radio transmitter have to be linear,which is to say for example that the functional relationship between theoutput power of the PA and the input power of the PA is a straight linefor all possible power levels. In addition, the phase shift of the inputsignal through the PA has to be constant for all possible power levels.

Departures from amplitude linearity and phase constancy introducedistortion into the PA's output signal, such as spectral broadening thatcan disturb nearby communication channels. Amplitude/phase distortion(vector distortion) in the transmitter can also increase the bit errorrate (BER) of the communication system, e.g., degrading the audioquality of a voice call or reducing the speed of an internet connection.

In general, the likelihood of proper transmitter performance can beincreased by including in the transmitter a transmitter observationreceiver (TOR) that samples the output signal of the PA and generates acompensation signal that is fed back to the modulator, PA, and/or othertransmitter components to correct the PA's output signal. In effect, thecompensation signal pre-distorts the transmitter input signal such thatthe PA's output signal is apparently undistorted. Since transmitterdistortion typically arises mainly in the PA, a signal acquired afterthe PA is fed back and compared with the transmitter input signal aspart of the pre-distortion process.

FIG. 1 is a block diagram of an arrangement 100 that is an example of apre-distortion-compensated transmitter having an antenna 102, a coupler104, a power amplifier 106, a modulator 108, and a TOR 110. The PA 106and modulator 108 can be considered the “transmit path” of thearrangement 100. It will be understood that the modulator 108 typicallyincludes oscillators and other components not shown and that themodulator 108 generally represents the base-band processing andup-conversion processing applied to the input signal. As seen in FIG. 1,the TOR 110 samples the transmitted signal generated by the transmitpath through the operation of the coupler 104 and provides acompensation signal to the modulator 108.

Currently available pre-distortion-compensated transmitters aregenerally designed to operate over a small range of transmittedfrequencies, such as a communication band of a communication system. Forexample, the Long Term Evolution (LTE) communication system currentlybeing standardized by the Third Generation Partnership Project (3GPP)has a communication Band 1 that covers 2110-2170 megahertz (MHz). Boththe forward transmit path and the feedback compensation path in thetransmitter are effectively tuned to the same range of frequencies, andcannot be deployed to support other frequency ranges, e.g., othercommunication bands. The typical transmitter operation is constrained toa single (narrow) frequency range of interest as a result of spectrallinearity limitations of its various tuned circuits (e.g., narrow-bandfilters) and tunable circuits (e.g., voltage-controlled localoscillators). For example, amplitude and phase variation over frequencymakes linearization (pre-distortion) difficult over a broad range offrequencies, and an oscillator may be able to tune over only a fewhundred MHz.

FIG. 2 is a block diagram that depicts a known way to use a single TORin a single-frequency, multi-transmitter arrangement. The multipletransmitters generate respective signals having the same carrierfrequency, e.g., any carrier in a communication band, of a communicationsystem. In the arrangement 200 depicted in

FIG. 2, an antenna 202-1 receives output signals of a Tx 1 PA 206-1 andan antenna 202-2 receives output signals of a Tx 2 PA 206-2 that have arespective Tx 1 modulator 208-1 and a Tx 2 modulator 208-2. Couplers204-1, 204-2 provide portions of the output signals of the PAs to asingle TOR 210 through operation of a switch 212. The TOR 210 samplesthe output signal connected to it by the switch 212 without needingtuning and provides a compensation signal to the respective modulator.In this way, the single TOR 210 is essentially time-shared sequentiallybetween the PAs 206-1, 206-2, each PA producing a signal in the samefrequency range. It is believed that such an arrangement was availablefrom Nortel in its CDMA tri-sector radio.

The frequency limitations of TORs and pre-distortion-compensatedtransmitters are becoming more serious problems as the number and rangeof available communication bands around the world increases. Currentlyavailable pre-distortion-compensated transmitters require redesign,modification and re-banding to operate in new communication bands, andthis increases the cost of designing and supporting communicationsystems.

SUMMARY

Problems and disadvantages of previous transmitters are overcome bymethods and arrangements in accordance with this invention.

In accordance with aspects of this invention, there is provided anarrangement for a pre-distortion-compensated transmitter for acommunication system. The arrangement includes an electronic processorcircuit configured for converting a base-band signal to be transmittedto a spectrally shifted, pre-distorted signal to be transmitted based onat least one compensation signal; a power amplifier configured forgenerating an amplified version of the spectrally shifted, pre-distortedsignal to be transmitted, where the amplified version is in onefrequency range of a plurality of frequency ranges used in thecommunication system; a coupler configured for generating a samplesignal from the amplified version; and a transmitter observationreceiver (TOR) configured for receiving the sample signal and generatingat least one compensation signal based on the sample signal. The atleast one compensation signal is generated such that a signal to betransmitted that is within a bandwidth that simultaneously encompassesmultiple frequency ranges is compensated. The electronic processorcircuit converts the base-band signal to be transmitted such that arelationship between the base-band signal to be transmitted and thesample signal is substantially linear with constant phase.

Also in accordance with aspects of this invention, there is provided amethod of pre-distortion-compensating a signal to be transmitted for acommunication system. The method includes converting a base-band signalto be transmitted to a spectrally shifted, pre-distorted signal to betransmitted based on at least one compensation signal; generating anamplified version of the spectrally shifted, pre-distorted signal to betransmitted, where the amplified version is in one frequency range of aplurality of frequency ranges used in the communication system;generating a sample signal from the amplified version; and generating atleast one compensation signal based on the sample signal such that asignal to be transmitted that is within a bandwidth that simultaneouslyencompasses multiple frequency ranges is compensated. The base-bandsignal to be transmitted is converted such that a relationship betweenthe base-band signal to be transmitted and the sample signal issubstantially linear with constant phase.

BRIEF DESCRIPTION OF THE DRAWINGS

The several objects, features, and advantages of this invention will beunderstood by reading this description in conjunction with the drawings,in which: FIG. 1 is a block diagram of a known single-frequencypre-distortion-compensated transmitter;

FIG. 2 is a block diagram of a single-frequency, multi-transmitterarrangement having a shared observation receiver;

FIG. 3 is a block diagram of a multi-band pre-distortion-compensatedtransmitter having a wideband analog observation receiver;

FIG. 4 is a block diagram of a multi-band pre-distortion-compensatedtransmitter having multiple observation receivers;

FIG. 5A is a block diagram of a pre-distortion-compensated transmitterhaving a tunable analog observation receiver;

FIG. 5B is a block diagram of a tuning block suitable for apre-distortion-compensated transmitter having a tunable observationreceiver;

FIGS. 6A, 6B are block diagrams of multi-band pre-distortion-compensatedtransmitters having tunable digital observation receivers;

FIG. 7 is a schematic diagram of a programmable digital down-converterfor a pre-distortion-compensated transmitter;

FIG. 8 is a diagram of an example of an LTE cellular communicationsystem; and

FIG. 9 is a flow chart of a method of pre-distortion-compensating asignal to be transmitted for a communication system.

DETAILED DESCRIPTION

This invention can be implemented in many types of communication systemthat use pre-distortion compensation of a signal transmitter. Thisdescription of examples of embodiments of the invention refers to theaccompanying drawings, in which the same or similar reference numbers indifferent drawings identify the same or similar components.

In response to the increasing number and range of availablecommunication bands around the world, transmitters capable of operatingin multiple communication bands are beginning to be developed. TORs canimprove such multi-band transmitters, and can be included in multi-bandtransmitters in a number of ways.

FIG. 3 is a block diagram of an arrangement 300 that is an example of apre-distortion-compensated transmitter having a single TOR that musthave sufficient bandwidth to see all relevant communication bands andall related distortion if it is to be able to compensate a signal to betransmitted that is within a bandwidth that simultaneously encompassesall relevant communication bands. The transmitter 300 has an antenna302, a coupler 304, a PA 306, and a base-band digital processor 308. ThePA 306 and processor 308 can be considered the transmit path of thearrangement 300. A TOR 310 depicted in FIG. 3 includes a widebanddown-converter 312, such as a wideband quadrature demodulator, and awideband analog-to-digital converter (ADC) 314 that converts thewideband analog signal produced by the down-converter 312 into a digitalwideband compensation signal provided to the processor 308.

As described above, a TOR is generally specifically tuned to operate inone frequency range, such as a part or all of one communication band,due to very stringent analog performance (gain and phase) requirements,and this currently makes it difficult to implement the single TOR 310for operation over multiple communication bands. The bandwidth needed bythe TOR 310 depends on the frequency range within which the signal to betransmitted by the transmitter 300 can be found, which can be abandwidth that simultaneously encompasses a plurality of communicationbands.

For example, if the transmitter 300 is configured for dual-bandoperation, e.g., to generate a 40-MHz-wide signal in Band 3 and a40-MHz-wide signal in Band 1, then the TOR 310 must generate acompensation signal such that those signals to be transmitted can becompensated, which in this example is a compensation signal within abandwidth that simultaneously encompasses both Band 1 and Band 3. Thecompensation signal is thus generated in a bandwidth of at least 1095MHz (i.e., (2170-1805 MHz)×3). To have such a wide bandwidth, the TOR310 requires significant power, circuit area, and cost, and optimization(for gain flatness, phase linearity, etc.) of the TOR 310 over such awide bandwidth is difficult. The difficulties increase dramatically asthe bandwidth within which the compensation signal must be generatedincreases, e.g., in a dual-band transmitter that is expected to operatein any two communication bands over a wide frequency range, such as1805-2170 MHz, or Bands 3, 9, 35, 39, 33, 37, 2, 36, 34, 4, and 1 in anLTE communication system. It will be appreciated that other frequencyranges and communication bands can be used as examples.

One way to overcome the difficulties of a single, wideband TOR 310 is touse multiple TORs, each optimized for a respective communication band orportion of the total transmitter bandwidth. Such an arrangement isdepicted in FIG. 4, which is a block diagram of an arrangement 400 thatis an example of a pre-distortion-compensated transmitter having twoTORs 410-1, 410-2. The transmitter 400 has an antenna 402, couplers404-1, 404-2, a PA 406, and a base-band digital processor 408. Each ofthe TORs 410-1, 410-2 includes a respective down-converter 412-1, 412-2and a respective ADC 414-1, 414-2 that need to operate over onlyrespective frequency ranges Range 1, Range 2, each of which is typicallymuch less than the transmitter's total bandwidth. Accordingly, thedown-converters 412 and ADCs 414 can be implemented more easily than thewideband down-converter 312 and wideband ADC 314.

Compared with the transmitter 300, the transmitter 400 eliminates therequirement for a TOR 310 that generates a compensation signal suitablefor a signal to be transmitted that is within a very wide bandwidth,e.g., within a bandwidth that simultaneously encompasses pluralcommunication bands. For example, if the transmitter 400 is configuredto generate a 40-MHz-wide signal in Band 3 and a 40-MHz-wide signal inBand 1, then the bandwidth of each of the TORs 410-1, 410-2 needs to beonly at least 120 MHz (40 MHz×3). Although it is easier to optimize theTORs 410 relative to the TOR 310, the transmitter 400 must have twoTORs, and in general as many TORs as signals in the transmitter'smulti-band signal to be transmitted, which imposes their associatedsignificant power, area, and cost requirements on the transmitter 400.In addition, the multiple TORs in the transmitter 400 still must beoptimized for specific frequencies or frequency ranges.

The arrangements depicted in FIGS. 3 and 4 can be further improved toenable compensating a signal to be transmitted that is within a widesimultaneous bandwidth and achieve efficient multi-band transmitteroperation as described below.

FIG. 5A is a block diagram of an arrangement 500 that is an example of apre-distortion-compensated transmitter having a single TOR that issequentially time-shared among multiple frequency ranges, resulting ingeneration of a compensation signal suitable for compensating atransmitted signal that is within a bandwidth that can simultaneouslyencompass a plurality of communication bands of the communicationsystem. The transmitter 500 has an antenna 502, a coupler 504, a PA 506,and a base-band digital processor 508. A TOR 510 depicted in FIG. 5Aincludes a down-converter 512, an ADC 514, and a local oscillator (LO)516 or other device that selects the operating frequency range of thedown-converter 512. It will be understood that the LO 516 can beconsidered to part of the down-converter 512.

The base-band processor 508 is typically configured to receive acomplex-valued input signal and the fed-back compensation signal, and tooutput a pre-distorted, up-converted signal. Although FIG. 5A depicts anup-converted, pre-distorted signal provided directly to the PA 506, itwill be understood that the pre-distorted signal can be a base-band orintermediate-frequency (IF) signal that is spectrally shifted bysuitable components (not shown) as appropriate. Thus, it will further beunderstood that the processor 508 includes one or more suitable ADCs anddigital-to-analog converters (DACs) for converting signals from analogform to digital form and vice versa, as needed.

It will also be understood that the pre-distorted signal generated bythe processor 508 is obtained by applying a suitable pre-distortionfunction to the input signal, advantageously in the digital domain. Thepre-distortion function is such that the relationship between the inputsignal and samples of the PA output signal is substantially linear withconstant phase. The pre-distortion function initially can be apredetermined function (e.g., based on a model of the PA) that can thenbe adapted based on the comparison of the complex input signal with thefed-back sample of the output signal. In this way, compensation signalsare generated in the digital domain, even compensation signals that donot strictly comply with the Nyquist criterion and even compensationsignals that may linearize transmitted signals in multiple bands basedon the transmitted signal in one of those bands.

The power amplifier generates an amplified version of the spectrallyshifted, pre-distorted signal to be transmitted in one communicationband of a plurality of communication bands used in the communicationsystem. As depicted in FIG. 5A, the TOR 510 advantageously can beoptimized for a bandwidth or frequency range that is sufficient to coverthe widest communication band of interest to the transmitter 500, and bysuitably tuning the LO 516, that bandwidth can be time-shared among allcommunication bands covered by the transmitter 500. It will beappreciated that the success of the arrangement depicted in FIG. 5Adepends on the optimization of the TOR 510 for all communication bandscovered by the transmitter 500. The selection of which band to observeis nominally achieved by simply tuning the LO 516, but other tuningcomponents 518 may need to be added or removed from the TOR 510 tocompensate for different circuit operation/performance in the differentbands and obtain desired performance at the different frequencies.

FIG. 5B depicts an example of an optional tuning block 518 that issuitable for a pre-distortion-compensated transmitter having a tunableobservation receiver, such as the arrangement depicted in FIG. 5A. Ingeneral, tuning components can include capacitors and/or inductors thatare selectively included/excluded from the TOR 510 by one or moresuitable switches or multiplexers, although as depicted in FIG. 5B, thetuning components 518 can be organized into an amplitude equalizer,comprising a resistor-inductor-capacitor (RLC) network having valuesappropriate for the particular frequency range, and a group-delayequalizer, comprising an LC network with suitable values, that need notbe switched in and out of the TOR 510. Even a well-designed widebandanalog TOR will show a reduction in gain as the input frequencyincreases (e.g., as the TOR changes from observing frequencies aroundBand 3 to frequencies around Band 1). Accordingly, the tuning block 518is one form of an analog frequency equalizer that can compensate forgain and phase variations with frequency of the TOR. It will beunderstood that many electrically equivalent arrangements can be used.An important advantage of a transmitter such as that depicted in FIG. 5Ais its reduction of the number of observation receivers to one receiverthat is configured for receiving the samples of the PA output signal andgenerating at least one compensation signal based on the samples suchthat a signal to be transmitted that can be anywhere within a bandwidththat simultaneously encompasses multiple communication bands iscompensated. This saves power/area/cost in exchange for requiring thereceiver 510 to be tuned to cover the desired frequency range of thetransmitted signal, e.g., multiple communication bands or even multipleportions of a single band.

The arrangement in FIG. 5A can thus be seen as time-sharing a single TOR510 across more than one communication band or portions of a frequencyrange by changing the LO frequency and possibly adjusting tuningcomponents. As described above, tuning an analog TOR typically requiresdifferent matching components for different frequency ranges ofoperation, but as illustrated by FIG. 5A, an analog TOR can be used formultiple frequency ranges by setting the LO to new frequencies andselecting and adjusting suitable tuning components.

The arrangement depicted in FIG. 5A can be further improved as describedbelow in connection with FIGS. 6A, 6B. FIG. 6A is a block diagram of anarrangement 600 that is an example of a pre-distortion-compensatedtransmitter having a TOR 610 that includes a digital down-converter 612,such as a suitably programmed digital processor circuit, and a widebandADC 614. The TOR 610 is configured for receiving the samples of the PAoutput signal and generating at least one compensation signal based onthe samples. The at least one compensation signal is generated such thata signal to be transmitted that is within a bandwidth thatsimultaneously encompasses multiple communication bands or frequencyranges is compensated. It will be noted in comparing the TORs 510, 610that the sampling rate of the ADC 614 is generally greater than thesampling rate of the ADC 514. Wideband ADCs 614 suitable for use incurrent cellular radio communication systems are commercially available,for example from National Semiconductor Corp., which is now part ofTexas Instruments Inc., Dallas, Tex., U.S.A. It will also be noted thatFIG. 6A does not explicitly show a LO as FIG. 5A does because the TOR610 preferably can be implemented with a fixed-frequency LO, with tuningof the TOR 610 implemented digitally rather than by tuning the LO.Nevertheless, the artisan will understand that other arrangements arepossible.

In the transmitter 600, filtering and tuning of the sampled transmittedsignal preferably is moved to the digital domain. In this way, therepeatability and configurability of digital-domain processing enableseasily changing which frequency range, e.g., which communication band,is observed by the TOR 610. By using a digital down-converter 612,errors that would be caused by analog components (e.g., due to time,voltage, and/or temperature variations) are not promulgated back throughsignals on the transmit path. Moreover, the response of the transmittercan be of the same quality across a wide frequency range, such as aplurality of communication bands. As noted above, TORs that employanalog components generally must be carefully optimized even for asingle communication band, and behave differently (and introduce errors)when used at other frequencies. The higher quality of the compensationsignal enables the base-band digital processor 608 to achieve a higherquality relationship between the transmitter's input signal and sampledoutput signal.

The wideband ADC 614 and digital down-converter 612 enable thearrangement 600 to operate in multiple communication bands in atime-shared way as the filter/tuner stage 612 selectively observes onecommunication band at a time. Thus, the arrangement 600 has power andspace advantages over a single-band pre-distortion-compensatedtransmitter, such as that described in U.S. patent application No.13/128,466 filed on Sep. 21, 2011, by Bradley John Morris et al. for“Method and Frequency Agile Pre-Distorted Transmitter Using ProgrammableDigital Up and Down Conversion”, which is a national phase ofInternational Application PCT/IB2010/002941 filed on Nov. 18, 2010. U.S.patent application No. 13/128,466 is incorporated in this application byreference.

Moreover, the arrangement 600 also has advantages over the transmitter500 described above in that difficulties arising from re-tuning a TORfor different communication bands can be substantially eliminated by thedigital down-converter 612, whose tuning parameters, filter response,etc. can easily be configured as necessary for each band. A suitabledigital down-converter 612 is described in U.S. patent application No.13/130,211 filed on Sep. 9, 2011, by Bradley John Morris et al. for“Methods and Systems for Programmable Digital Down-Conversion”, which isa national phase of International Application PCT/IB2010/002927 filed onNov. 18, 2010. U.S. patent application No. 13/130,211 is incorporated inthis application by reference.

FIG. 6B is a block diagram of an arrangement 600′ that is an example ofa pre-distortion-compensated transmitter having a TOR 610′ that includesplural digital down-converters 612-1, 612-2 and a wideband ADC 614′,such as the circuits described above in connection with FIG. 6A. The TOR610′ is configured for receiving the sample signal and generating atleast one compensation signal based on samples of the PA output signal.The at least one compensation signal is generated such that a signal tobe transmitted that is within a bandwidth that simultaneouslyencompasses multiple communication bands or frequency ranges iscompensated. As in FIG. 6A, it will be noted that FIG. 6B does notexplicitly show a LO as FIG. 5A does because the TOR 610′ preferably canbe implemented with a fixed-frequency LO, with tuning of the TOR 610′implemented digitally rather than by tuning the LO.

The plural down-converters 612-1, 612-2 can be configured in severalways for continuous observation of a given frequency range, such as acommunication band or plural communication bands. It will be understoodthat FIG. 6B depicts two down-converters 612 but more can be included inthe arrangement 600′. The arrangement 600′ is relatively more efficientthan other possible arrangements in that it shares its analog componentsand wideband ADC among replicated digital functionality. In addition,the transmitter 600′ can be advantageous with respect to the transmitter600 in that the TOR 610′ can continuously observe the transmitted signalby using as many digital down-converters 612 as needed.

FIG. 7 is a schematic diagram of a programmable digital down-converter612 that is suitable for a pre-distortion-compensated transmitter, suchas the arrangements 600, 600′. The converter 612 includes a complexfrequency range or band selection filter 702, a digital down-sampler704, and a complex base-band tuner 706. The complex baseband tuner 706can alternatively be included in the base-band digital processor 608,608′. The functionality of the filter 702 and down-sampler 704 can beimplemented with a polyphase filter.

The down-sampler 704 is configured to generate a down-sampled signalthat includes one sample for each N samples in a digital signal input tothe down-sampler, where N is an integer that is greater than or equal totwo. Of course, it is preferable for N to be an integer power of two,but a rate-change filter can be included in the down-converter 612 tohandle conversion of the sampling rate of the input signal provided tothe down-converter divided by N to a desired sampling rate of the outputsignal generated by the down-converter.

It will be appreciated that a filter is not required before the ADC 614when there is minimal interference (e.g., something other than thetransmitted signal) from the antenna 602 coupled into the feedback path.All required filtering can then be achieved digitally duringdown-conversion, for example, by judicious selection of polyphase filtercoefficients in the programmable digital down-converter 612.

FIG. 8 is a diagram of an example of an LTE cellular communicationsystem 800 that includes user equipments (UEs) 810, 820, a radio accessnetwork (RAN) that includes a plurality of evolved Node B (eNodeBs0, orbase stations, 130 1, 130 2, . . . , 130 N, and a core network (CN) thatincludes a serving gateway (SGW) node 140 and a packet data network 150.Other nodes can also be provided in the system 800.

Each eNodeB 130 1, 130 2, . . . , 130 N serves a respective geographicalarea that is divided into one or more cells. An eNodeB can use one ormore of the pre-distortion-compensated transmitters described above andantennas at one or more sites to transmit information into its cell(s),and different antennas can transmit respective, different pilot andother signals. Neighboring eNodeBs are coupled to each other by anX2-protocol interface that supports active-mode mobility of the UEs. AneNodeB controls various radio network functions, including for examplesingle-cell radio resource management (RRM), such as radio access bearersetup, handover, UE uplink/downlink scheduling, etc. Each eNodeB alsocarries out the Layer-1 functions of coding, decoding, modulating,demodulating, interleaving, de-interleaving, etc.; and the Layer-2retransmission mechanisms, such as hybrid automatic repeat request(HARQ), and functions of radio link control (RLC) and RRC. The eNodeBs130 1, 130 2, . . . , 130 N are coupled to one or more SGWs 140 (onlyone of which is shown in FIG. 8).

The network 800 can exchange information with one or more other networksof any type, including a local area network (LAN); a wide area network(WAN); a metropolitan area network; a telephone network, such as apublic switched terminal network or a public land mobile network; asatellite network; an intranet; the Internet; or a combination ofnetworks. It will be appreciated that the number of nodes illustrated inFIG. 8 is simply an example. Other configurations with more, fewer, or adifferent arrangement of nodes can be implemented. Moreover, one or morenodes in FIG. 8 can perform one or more of the tasks described as beingperformed by one or more other nodes in FIG. 8. For example, parts ofthe functionality of the eNodeBs can be divided among one or more basestations and one or more radio network controllers, and otherfunctionalities can be moved to other nodes in the network.

FIG. 9 is a flow chart of an example of a method ofpre-distortion-compensating a signal to be transmitted for acommunication system. The method includes converting (step 902) abase-band signal to be transmitted to a spectrally shifted,pre-distorted signal to be transmitted based on at least onecompensation signal, for example by a base-band digital processor 608,608′. The method also includes generating (step 904) an amplifiedversion of the spectrally shifted, pre-distorted signal to betransmitted, for example by a PA 606, 606′, where the amplified versionis in one communication band of a plurality of communication bands usedin the communication system. The method also includes generating (step906) a sample signal from the amplified version, for example by acoupler 604, 604′. The method also includes generating (step 608) atleast one compensation signal based on the sample signal such that asignal to be transmitted that is within a bandwidth that simultaneouslyencompasses multiple communication bands or frequency ranges iscompensated, for example by a TOR 610, 610′. Generating the at least onecompensation signal includes converting the sample signal into a digitalsample signal, and generating the at least one compensation signal basedon the digital sample signal. As described above, the base-band signalto be transmitted is converted such that a relationship between thebase-band signal to be transmitted and the sample signal issubstantially linear with constant phase.

Also as described above, generating the at least one compensation signalcan include generating a plurality of compensation signals, each ofwhich is optimized for a respective frequency range in a plurality ofcommunication bands, and each frequency range can correspond to arespective one of the plural communication bands in a communicationsystem, such as that depicted in FIG. 8. The sample signal can beconverted into the digital sample signal by a wideband ADC 614, 614′ orequivalent device. Generating the at least one compensation signal canalso include tuning to different frequency ranges in the bandwidth byselecting at least one tuning parameter and filter response or analogcompensation component.

It is expected that this invention can be implemented in a wide varietyof environments, including for example mobile communication devices. Itwill be appreciated that procedures described above are carried outrepetitively as necessary. To facilitate understanding, many aspects ofthe invention are described in terms of sequences of actions that can beperformed by, for example, elements of a programmable computer system.It will be recognized that various actions could be performed byspecialized circuits (e.g., discrete logic gates interconnected toperform a specialized function or application-specific integratedcircuits), by program instructions executed by one or more processors,or by a combination of both. Many communication devices can easily carryout the computations and determinations described here with theirprogrammable processors and application-specific integrated circuits.

Moreover, the invention described here can additionally be considered tobe embodied entirely within any form of computer-readable storage mediumhaving stored therein an appropriate set of instructions for use by orin connection with an instruction-execution system, apparatus, ordevice, such as a computer-based system, processor-containing system, orother system that can fetch instructions from a medium and execute theinstructions. As used here, a “computer-readable medium” can be anymeans that can contain, store, or transport the program for use by or inconnection with the instruction-execution system, apparatus, or device.The computer-readable medium can be, for example but not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, or device. More specific examples (anon-exhaustive list) of the computer-readable medium include anelectrical connection having one or more wires, a portable computerdiskette, a RAM, a ROM, an erasable programmable read-only memory (EPROMor Flash memory), and an optical fiber.

Thus, the invention may be embodied in many different forms, not all ofwhich are described above, and all such forms are contemplated to bewithin the scope of the invention. For each of the various aspects ofthe invention, any such form may be referred to as “logic configured to”perform a described action, or alternatively as “logic that” performs adescribed action.

It is emphasized that the terms “comprises” and “comprising”, when usedin this application, specify the presence of stated features, integers,steps, or components and do not preclude the presence or addition of oneor more other features, integers, steps, components, or groups thereof.

The particular embodiments described above are merely illustrative andshould not be considered restrictive in any way. The scope of theinvention is determined by the following claims, and all variations andequivalents that fall within the range of the claims are intended to beembraced therein.

What is claimed is:
 1. An arrangement for a pre-distortion-compensatedtransmitter for a communication system, comprising: an electronicprocessor circuit configured for converting a base-band signal to betransmitted to a spectrally shifted, pre-distorted signal to betransmitted based on at least one compensation signal; a power amplifierconfigured for generating an amplified version of the spectrallyshifted, pre-distorted signal to be transmitted, wherein the amplifiedversion is in one frequency range of a plurality of frequency rangesused in the communication system; a coupler configured for generating asample signal from the amplified version; and a transmitter observationreceiver (TOR) configured for receiving the sample signal and generatingat least one compensation signal based on the sample signal; wherein theat least one compensation signal is generated such that a signal to betransmitted that is within a bandwidth that simultaneously encompassesmultiple frequency ranges is compensated, and the electronic processorcircuit converts the base-band signal to be transmitted such that arelationship between the base-band signal to be transmitted and thesample signal is substantially linear with constant phase.
 2. Thearrangement of claim 1, wherein the TOR includes a widebandanalog-to-digital converter (ADC) configured for converting the samplesignal into a digital sample signal, and at least one digitaldown-converter configured for generating the at least one compensationsignal; and the electronic processor circuit converts the base-bandsignal to be transmitted such that a relationship between the base-bandsignal to be transmitted and the sample signal is substantially linearwith constant phase.
 3. The arrangement of claim 2, wherein the TORincludes a plurality of digital down-converters, each of which isoptimized for a respective frequency range in the plurality of frequencyranges.
 4. The arrangement of claim 3, wherein each frequency rangecorrespond to a respective one of a plurality of communication bands. 5.The arrangement of claim 1, wherein the TOR is configured for tuning todifferent frequency ranges in the bandwidth by selectively adjusting atleast one tuning component of the TOR.
 6. A method ofpre-distortion-compensating a signal to be transmitted for acommunication system, comprising: converting a base-band signal to betransmitted to a spectrally shifted, pre-distorted signal to betransmitted based on at least one compensation signal; generating anamplified version of the spectrally shifted, pre-distorted signal to betransmitted, wherein the amplified version is in one communication bandof a plurality of communication bands used in the communication system;generating a sample signal from the amplified version; and generatingthe at least one compensation signal based on the sample signal suchthat a signal to be transmitted that is within a bandwidth thatsimultaneously encompasses multiple frequency ranges is compensated;wherein the base-band signal is converted such that a relationshipbetween the base-band signal to be transmitted and the sample signal issubstantially linear with constant phase.
 7. The method claim 6, whereingenerating the at least one compensation signal includes converting thesample signal into a digital sample signal, and generating the at leastone compensation signal based on the digital sample signal; and thebase-band signal to be transmitted is converted such that a relationshipbetween the base-band signal to be transmitted and the sample signal issubstantially linear with constant phase.
 8. The method of claim 6,wherein generating the at least one compensation signal includesgenerating a plurality of compensation signals, each of which isoptimized for a respective frequency range in the plurality of frequencyranges.
 9. The method of claim 8, wherein each frequency rangecorresponds to a respective one of a plurality of communication bands.10. The method of claim 6, wherein generating the at least onecompensation signal includes tuning to different frequency ranges in thebandwidth by selecting at least one tuning component.